SmartGit/Hg is a graphical user interface for Git and Mercurial which can work with SVN
repositories.
It supports cloning from common repository providers (e.g.,
GitHub,
Assembla),
assists Git newbies,
and also offers the advanced, powerful Git features.
It provides several tools to help create clean commits, for example by
allowing the user to commit just parts of changes files and reordering
and squashing unpushed commits.
If you are using GitHub or GitHub Enterprise,
SmartGit/Hg can work easily with pull
requests (creation,
resolving) and commit comments.
SmartGit/Hg ships with a built-in SSH client,
file comparer, and merge tool which are capable
of syntax coloring for many languages.

PHP Git Client Class is a class for accessing files in Git repositories. It can connect to a remote repository and checkout files similar to the git clone command, and retrieve the log of changes to a file.

A tool for editing version-control repository history, reposurgeon enables risky operations that version-control systems don't want to let you do, such as editing past comments and metadata and removing commits. It works with any version control system that can export and import git fast-import streams, including git, hg, bzr, CVS, and RCS. It can also read Subversion dump files directly, and can thus be used to script production of very high-quality conversions from Subversion to any supported DVCS.

deltasql is a tool to synchronize databases with
source code, which helps to keep database
evolution under control. While developing
mid-sized or big applications, developers make
changes to the data model that go along with
changes to the source code. From time to time,
branches of source code are done to stabilize the
code that will go to production. A sort of data
model branch is also needed. deltasql provides a
simple way to collect all scripts that change the
data model and means to handle data model
branches. The deltasql server runs on Apache and
is backed by MySQL.

OpenGrok is a fast and usable source code search and cross reference engine. It helps you search, cross-reference, and navigate your source tree. It can understand various program file formats and version control histories like Mercurial, Bazaar, Git, ClearCase, Perforce, SCCS, RCS, CVS, or Subversion. In other words, it lets you grok (profoundly understand) the source.

cvs-fast-export analyzes a collection of RCS files in a CVS repository (or outside of one) and, when possible, emits an equivalent history in the form of a fast-import stream. Not all possible histories can be rendered this way; the program tries to emit useful warnings when it can't. The program can also produce a visualization of the resulting commit DAG in the DOT format handled by the graphviz suite. The package also includes cvssync, a tool for mirroring masters from remote CVS hosts.

Tada is a Git client that handles multiple Git repositories simultaneously. Its user interface is based on consoloid technology, so it can be controlled with words in addition to the mouse pointer. It works on the desktop as well as on mobile devices.

SVNManager is a Web-based administration tool for
servers that host Subversion repositories. With
this tool, users can remotely create repositories,
give access rights to users and groups, dump and
load repositories, and invite users to create an
account on the server.